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author | Jakub Kicinski <kuba@kernel.org> | 2022-06-09 16:38:15 -0700 |
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committer | Jakub Kicinski <kuba@kernel.org> | 2022-06-09 16:38:15 -0700 |
commit | a98a62e456e25048e8d64ec452a1c713169d3517 (patch) | |
tree | 52bc4063aae5015ef28f174d9de409788ee9e0a4 /Documentation/driver-api/tty/index.rst | |
parent | net: macb: change return type for gem_ptp_set_one_step_sync() (diff) | |
parent | Merge tag 'net-5.19-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net (diff) | |
download | linux-dev-a98a62e456e25048e8d64ec452a1c713169d3517.tar.xz linux-dev-a98a62e456e25048e8d64ec452a1c713169d3517.zip |
Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
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Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'Documentation/driver-api/tty/index.rst')
-rw-r--r-- | Documentation/driver-api/tty/index.rst | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/Documentation/driver-api/tty/index.rst b/Documentation/driver-api/tty/index.rst new file mode 100644 index 000000000000..2d32606a4278 --- /dev/null +++ b/Documentation/driver-api/tty/index.rst @@ -0,0 +1,73 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=== +TTY +=== + +Teletypewriter (TTY) layer takes care of all those serial devices. Including +the virtual ones like pseudoterminal (PTY). + +TTY structures +============== + +There are several major TTY structures. Every TTY device in a system has a +corresponding struct tty_port. These devices are maintained by a TTY driver +which is struct tty_driver. This structure describes the driver but also +contains a reference to operations which could be performed on the TTYs. It is +struct tty_operations. Then, upon open, a struct tty_struct is allocated and +lives until the final close. During this time, several callbacks from struct +tty_operations are invoked by the TTY layer. + +Every character received by the kernel (both from devices and users) is passed +through a preselected :doc:`tty_ldisc` (in +short ldisc; in C, struct tty_ldisc_ops). Its task is to transform characters +as defined by a particular ldisc or by user too. The default one is n_tty, +implementing echoes, signal handling, jobs control, special characters +processing, and more. The transformed characters are passed further to +user/device, depending on the source. + +In-detail description of the named TTY structures is in separate documents: + +.. toctree:: + :maxdepth: 2 + + tty_driver + tty_port + tty_struct + tty_ldisc + tty_buffer + tty_internals + +Writing TTY Driver +================== + +Before one starts writing a TTY driver, they must consider +:doc:`Serial <../serial/driver>` and :doc:`USB Serial <../../usb/usb-serial>` +layers first. Drivers for serial devices can often use one of these specific +layers to implement a serial driver. Only special devices should be handled +directly by the TTY Layer. If you are about to write such a driver, read on. + +A *typical* sequence a TTY driver performs is as follows: + +#. Allocate and register a TTY driver (module init) +#. Create and register TTY devices as they are probed (probe function) +#. Handle TTY operations and events like interrupts (TTY core invokes the + former, the device the latter) +#. Remove devices as they are going away (remove function) +#. Unregister and free the TTY driver (module exit) + +Steps regarding driver, i.e. 1., 3., and 5. are described in detail in +:doc:`tty_driver`. For the other two (devices handling), look into +:doc:`tty_port`. + +Other Documentation +=================== + +Miscellaneous documentation can be further found in these documents: + +.. toctree:: + :maxdepth: 2 + + moxa-smartio + n_gsm + n_tty |